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Reversing Expectations: Dan Breecker Looks to the Present to Understand the Past

Dan Breecker

Most geologists can be forgiven for living in the past, but Dan Breecker is making a point of keeping focused on the present. Breecker, who joined the Jackson School of Geosciences as an assistant professor in 2009, concentrates on the interactions between climates, soils, and carbon dioxide (CO2) levels, and his research is helping to improve our understanding of historical and current climate change.

As a doctoral student at the University of New Mexico, Breecker began studying the formation of soil carbonates, which are rocks or minerals, such as calcite, found in the ground and dominated by carbon-based ions. Working with colleagues, he took measurements from modern soils from New Mexico to Saskatchewan, Canada to determine how and when during each year the carbonates formed. Then the geoscientists used stable isotope composition to compare them with estimated levels from the planet’s hottest “greenhouse” periods of the Paleozoic (255 million years ago) and Mesozoic (55 million years ago) eras.

“We didn’t even know what we were going to find,” Breecker says.

In fact, the team of researchers concluded that atmospheric carbon dioxide levels during the ancient greenhouse events were quite similar to projected climate-change scenarios for the year 2100, meaning we could be a lot closer to a hotter planet than we thought.

“It actually looks like the CO2 concentrations during the hothouse in the Mezozoic?-the greenhouse climates-?may not have been much higher than where we may be at the end of this century,” Breecker says.

Past studies have missed this association, partly because scientists assumed the carbonates’ CO2 levels represent a mean, or average, reading of conditions. But by studying modern soils, Breecker discovered that carbonates form during very hot and dry times when carbon dioxide concentrations are lower than during less extreme periods.

“The carbonates record this kind of anomalous time of year,” Breecker says, “and because they form during the extreme conditions, the atmospheric CO2 concentrations that you calculate are actually lower than they otherwise would be.”

The results, which were published in the Proceedings of the National Academy of Sciences in December 2009, supersede preceding reports on prehistoric CO2 levels. Previous studies suggested past greenhouse events occurred when atmospheric carbon dioxide reached 3,000 to 4,000 parts per million. Breecker’s findings update the greenhouse estimates to just 1,000 parts per million.

The data also correlates with levels detected from other proxies that preserve pieces of the geologic record. Scientists have studied fossil plants and leaves and other proxies and discovered evidence of the lower CO2 levels during greenhouse periods, but most geoscientists were unable to square those measurements with the previous observations taken from the ancient soils, or paleosols. Breecker’s work resolves the discrepancy.

“The concentrations we got from the paleosol carbonates are in better agreement with other proxies,” Breecker says. He adds that newer numerical models also support the findings.

The insight into the past is essential to our understanding of geologic processes in ancient eras. But Breecker also emphasizes the critical importance of the implications for the future and how we prepare for and continue to monitor climate change during the next century.

“I think that geologists who are doing most of this work are always excited about looking into the past,” Breecker says, “and I think there is a tendency to not spend quite enough time on the modern environments and to know what your proxies mean before you go ahead and collect some ancient samples that are going to tell you something about the past.

“The main motivation I use for my research,” he continues, “is to try to better understand and better predict climate change by calibrating these proxies and figuring out what they mean for past climates, so we can better understand the future.”

Breecker plans to continue examining past and present soils and CO2 levels. Along a related track, he is working with Jackson School colleague Jay Banner to study the formation of calcium carbonates in caves, which provide another measurement of ancient climate levels and their relation to modern conditions.

Breecker is also launching research on the Marais des Cygnes National Wildlife Refuge in Kansas, studying how soils of the native prairie sequester, or trap, carbon. Land managers have conventionally encouraged forestation, rather than prairie restoration, as a means to store carbon and offset human CO2 emissions. But Breecker has made initial observations suggesting that native grasslands store a much greater amount of carbon and organic matter than farmlands, and he believes further measurements could influence management strategies to store carbon and restore native prairies.

“I definitely think there’s work to be done here,” Breecker says, “and I think part of the reason is that everyone’s so focused on the past rather than what’s happening in the present.”

By Joshua Zaffos

For more information about the Jackson School contact J.B. Bird at jbird@jsg.utexas.edu, 512-232-9623.